In a food processor, whirl nuts, 3/4 cup sugar, and egg to a coarse paste.
Butter and flour a 12- by 15-inch baking sheet, plain or nonstick. Drop level tablespoons of pistachio mixture about 3 inches apart onto baking sheet. Sprinkle lightly with more sugar.
Bake cookies in a 325°oven until lightly browned, 14 to 18 minutes (10 to 12 minutes in a convection oven). Let cool on pan until firm, about 5 minutes. Slide a metal spatula under cookies to release; transfer to a rack. Serve warm or cool.